Although the men were only charged with stealing and laundering a total of £1.8 million, West Midlands Police believe up to £6 million of public funds could have been lost as a result of the fraud.

Astonbrook received £15 million in just over a year from the Government alone while Birmingham City Council also pumped £6 million into the organisation.

The six men were able to exploit failings by UKBA to check and monitor how the money was spent.

And incredibly, when an investigation was launched by the Home Office department, it was headed by a convicted conman – later jailed for committing two further frauds.

Wendy Bounds, Complex Casework Lawyer from West Midlands Crown Prosecution Service, said the defendants exploited a ‘‘lack of fiscal audit or fiscal control by the UKBA and the city council, and therefore, they were able to write cheques to themselves and to companies controlled by them.

‘‘They covered up their fraud by creating accounting documents which looked, on superficial examination, as legitimate.

“The money which they stole either went into their personal bank accounts, or was used to purchase properties or went abroad.”

The city council and UKBA launched an inquiry into the charity in 2007 after being contacted by a whistleblower.

But UKBA put Andrew Waldron in charge of its side of the investigation – unaware that he had been convicted in connection with lying on his CV in a previous job, as press officer for Gloucestershire Police.

Embarrassingly, Waldron was arrested part-way through the Astonbrook inquiry by West Midlands Police. He was later jailed for seven years for lying on his Home Office job CV and for a separate fraud committed while on bail.

Yesterday Mohammed Arwo and Abdi were sentenced to four and a half years and Ismail and Yassin received two and a half years.

Arwo was disqualified from being a director of a company for 10 years.

His brother Mustafe Hassan Arwo was sentenced to two years and Said was jailed for 15 months. They were both given seven years disqualifications.

Despite being made bankrupt in January 2006, Mohammed Arwo personally negotiated a contract with UKBA which paid the charity £15 million – £1.3 million a month – between May 2006 and July 2007.

It is understood that if he had declared his bankruptcy, or if UKBA had carried out even basic checks, the UKBA and city council contract would never have gone ahead.

Astonbrook, which had more than 3,000 clients on its book, was supposed to provide suitable accommodation to asylum seekers.

But they were often dumped into sub-standard properties with torn wallpaper, smashed windows and dangerous electrical wires hanging loose.

Arwo was originally a director of the Highgate and Erdington-based charity before becoming its chief executive in October 2003.

Yet he and fellow defendants were systematically redistrib

uting cash by sending cheques from Astonbrook to up to six Birmingham companies – which had links with some of the defendants.

Incredibly, the unsophisticated con was not spotted by UKBA which had carried out virtually no in-depth checks into Arwo’s background or the running of the company.

The charity later went into liquidation with the loss of scores of jobs, sparking public protests.

The police investigation was led by Detective Constable Mark Simmons, who died before the conclusion of the case, Detective Constable Andy Smith and Detective Sergeant Emma Hickl, from the force’s Economic Crime Unit.

Det Sgt Hickl said after sentencing: “The behaviour of these individuals was so audacious that they did not only exploit Birmingham City Council and UKBA, but ultimately every single tax payer in this country.

“They also showed complete disregard for the welfare of the asylum seekers they were paid to help in the first place.’’

A spokeswoman for the force said the team were in line for commendation awards, while Det Sgt Hickl paid tribute to DC Simmons, who died suddenly in June.

She said: ‘‘Mark worked tirelessly and conducted a painstaking investigation.

“The insurmountable evidence he gathered ensured these individuals were bought to justice and I know he would be delighted with today’s outcome.

“I am only sorry that he is not with us today to see all his hard work coming to fruition.”

A spokesman for Birmingham City Council said monitoring of service providers was now carried out on a monthly basis.

A UK Border Agency spokesperson said: “A performance management and monitoring regime, including regular inspections, has been implemented to ensure that suppliers are contractually compliant and held to account by UK Border Agency.”